A slide-fastener stringer, as this term is used herein, will be considered to consist of a pair of support tapes each of which can carry along a longitudinal edge confronting the other support tape, a row of spaced apart coupling members capable of interdigitating with the other row.
In its use such a stringer, consisting of two slide-fastener halves, can be provided with end-stop members at opposite ends of each or both rows to prevent withdrawal of a slider which rides along the rows. In a so-called "separable" slide fastener, these end-stop members can be connectable at one end of the stringer and can be disconnected to allow the slider to remain on only one of the slide-fastener halves in an open condition of the slide fastener.
The term coupling member is used herein to refer to a projection from the longitudinal edge of the other support tape and engage behind projections of the latter. The portions of the projections which thus interdigitate or engage are usually shaped so as to resist separation by forces applied transverse to the slide fastener axis or the rows of coupling members. These portions of the projections, referred to herein as coupling heads, can be affixed to the respective support tapes by shanks which extend inwardly beyond the edge and can straddle the opposite faces of the tape. Thus the coupling members can have a generally U-shaped configuration with the head formed at the bight of the U and the shanks constituting the legs thereof.
The support tapes can be woven or knitted and can even be a hybrid, i.e. partly woven and partly knitted, in each case with or without inlaid yarns, strands or filaments. When any of these latter terms are used herein, any other of them will be deemed equivalent. For example, the tapes can be knitted and/or woven from synthetic-resin monofilament, i.e. single strand threads, or can be formed from multistrand threads, generally designated as yarns.
Whatever the particular thread construction, the tape will have a mesh structure, either formed by the knit loops or by the crossing weft and warp of the weave. The mesh size is thus a function of the proximity of the yarns forming the mesh to one another.
Reference will also be made herein to the thermosetting of a tape. Thermosetting as this term is used herein will refer to the thermostabilization of the fabric structure which results from a combination of shrinking and stress-relieving in thermoplastic materials such as the filaments, threads or yarns, with or without the formation of fusion bonds at points at which threads cross over one another. Condensation of the mesh refers to a reduction in the openings left in a fabric by virtue of a closer disposition of the strands forming the mesh.
In this description reference may also be made to a filler cord. A filler cord is usually a single strand or a woven or braided bundle of strands of synthetic-resin filaments or natural fiber, usually of a thickness greater than that of the strands making up the fabric tape and usually knitted or woven into the tape along the longitudinal edge at which the coupling members are mounted so that the shanks of the coupling member can straddle these cords as well.
Two or more such strands may also be provided, e.g. in a side-by-side relationship to form a cord or "bead."
Furthermore, these cords can be compressible so that the coupling head of one row, upon interdigitation with the coupling heads of the second row, also bear against the filler cord of this latter row.
Finally, with respect to the general nature of slide-fastener stringers, mention may be made of the fact that the slider can be of conventional design and hence will not be described or discussed in detail. However, it may be noted that the slide-fastener stringer can be formed substantially continuously and cut into lengths whereupon the slider and end-stop members can be applied to the end-stop members molded from the thermoplastic material of the coupling members or tape by the application of heat or pressure.
The particular type of slide fastener, with which the present invention is concerned, has a stringer which utilizes U-shaped coupling members of thermoplastic synthetic resins and support tapes of synthetic yarn or filaments whereby each coupling member is formed in the region of the bight with a coupling head and between the shanks of the U with a coupling eye, the shanks straddling the edge of the support tape and being fixed thereto.
Coupling members of this type are generally bent into the U configuration from generally flat members or "blanks" and the filler cord can be disposed in the coupling eye so that in the interdigitated state or upon deformation of the fastener in the fastener plane or out of the latter compression is applied to the filler cord.
In German patent document (printed application--Auslegeschrift) DE-AS No. 16 10 325, the blanks adapted to form the coupling members, while in a flat state, constitute the rungs of a ladder which included textile strands which interconnect these members even when they are bent into the U-configuration to straddle the tape. The coupling members are fixed in place by a sewing seam. This method of fabricating slide-fastener stringers has been found to be an expensive operation in part because of the time-consuming and laborious sewing step. However, of possible greater significance is the fact that the sewing operation has been found not to secure the coupling members to the tape with sufficient firmness. When transverse or bending stresses are applied to such stringers, the stability in the closed state is lost. In practice, therefore, such systems have scarcely been used.
A more common system is that described in German patent document (open application--Offenlegungsschrift) DE-OS No. 27 22 054 in which a textile cord is provided as an independent element upon which the U-shaped bent coupling members are applied. In this case, four textile strands are customarily embedded in the shanks so that two such strands traverse each shank of each coupling member on a single support tape.
The row of coupling members thus forms an independent assembly which can be connected with the support tape during the weaving or knitting process so that, for example, only weft yarns during weaving and corresponding yarns during knitting engage the filler cord and the strands mentioned above.
In the region of the attachment of the coupling members, there are no warp threads or yarns of the tape.
This construction, while highly desirable because of the reliability of the spacing of the coupling heads, has not been completely satisfactory because the fabrication technique is expensive by reason of the need to feed the entire coupling member assembly to the knitting machine or the loom.
Experience has shown that weaving or knitting machines which must be fed with foreign assemblies of complex shape and construction can only operate at low speeds. In addition, the formation of the assembly and the supply thereof to the tape-making machine has created problems.
Mention may also be made of the fact that when the stringer is subjected to transverse stress, i.e. tension, the filler cord and the shank-connecting strands must be able to take up the total stress. Singularities in the application of stress can normally be detected at which locations considerable shear is generated. Because of the manner in which the assembly is connected to the tape, there it little distribution of the stress to the tape itself.
Because of this concentration of stress, the structure of the tape and the connection, under transverse tension, may change and with time the stringer may become unusable.
Tests have shown, for example, that individual coupling members can twist out of position about the axis parallel to the axis of the stringer relative to the tape plane. Thus one can conclude that the connection coupling member of the tape is not sufficiently torsion resistant. When the slide fastener is used in garments, for example, it may open at a disadvantageous moment and the improper lie of the coupling member may result in inability to move the slider along the rows. If the dislocation remains the overall ability of the slide fastener to withstand transverse stress is reduced.
It has been proposed to decrease the transverse-tension and torsion sensitivity of such slide fasteners by providing grooves at the foot of each coupling member and introducing additional strands into the latter. This significantly increases the fabrication problems and does not give rise to a proportional improvement in the ability of the device to resist stress in the form of transverse tension or torque.
Finally, it may be noted that it has been proposed heretofore to form, by suitable injection molding machines and dies, coupling members directly upon the support tapes and in such configuration that they embrace the edges of the tape. This technique, however, has been found to be practical only for relatively large coupling members and has not been exploited with complete success for garment fasteners which must be of fine and reliable construction.